Mescaline (3,4,5-trimethoxyphenethylamine) is a naturally occurring psychedelic alkaloid of the phenethylamine class, known for its mind-altering effects similar to lysergic acid diethylamide, although LSD is 4000 times more potent than mescaline in producing altered states of consciousness. Mescaline is obtainable from peyote cactus (Lophophora williamsii) (1), which belongs to the Cactaceae family: it is slow growing in the desert zone along Texas and Mexico and has been used for centuries by the natives of Mexico and Southwestern United States for ceremonial purposes. It is also found in small amounts in certain members of the Fabaceae (bean) family, including Acacia berlandieri. Mescaline was first isolated and identified in 1897 by the German Arthur Heffter and first synthesized in 1919 by Ernst Späth: it had been used in the past for medical uses including treatment of alcoholism and depression with no notable results.

Mescaline is produced when products of natural mammalian catecholamine-based neuronal signaling such as dopamine and serotonin are subjected to additional metabolism via methylation, and its hallucinogenic properties stem from these very structural similarities. In plants, this compound may be the end product of a pathway utilizing catecholamines as a method of stress response, similar to how animals may release compounds such as cortisol when stressed. The in vivo function of catecholamines have not been investigated, but they may function as antioxidants , as developmental signals, and as integral cell wall components that resist degradation from pathogens. The deactivation of catecholamines via methylation produces alkaloids such as mescaline (2). Mescaline acts similarly to other psychedelic agents (3) . It binds to and activates the serotonin 5-HT2A receptor with a high affinity as a partial agonist. How activating the 5-HT2A receptor leads to psychedelia is still unknown, but it likely somehow involves excitation of neurons in the prefrontal cortex (4) . Mescaline is also known to bind to and activate the serotonin 5-HT2C receptor (5). In addition to serotonin receptor activity, mescaline also stimulates the dopamine receptors(6) . Whether mescaline possesses dopamine receptor agonist properties or initiates the release of dopamine remains unclear. Difluoro and trifluoromescaline have shown to be more potent than their unfluorinated analogue (7).

Mescaline experiences are deeply related with doses, however 100 mg are usually enough to observe its psychedelic activity. A mescaline or peyote trip uses to appear as far as 1 or 2 hours later and it can last up to 12 hours. Mescaline effects seem to manifest more clearly with eyes closed or under low lighting conditions and with the help of music (8); however, all of these visual descriptions are purely subjective. Trips are composed by three phases:
- Step 1 , physiological effects (about 30 minutes after the assumption, it last from 45 minutes to 1 hour ) : nausea , dizziness ,cardiovascular effects, which speed up the heartbeat and increase the blood pressure, eyes' pupils dilatation, blood sugar level and body temperature increase, heavy perspiration , neck and mandible muscles tensing. hunger , thirst and effort disappear (9) .
- Step 2 , psychic effects (1or 2,but also hours later): great rushes of energy and euphoria are described. Prominence of color is distinctive, appearing brilliant and intense. Recurring visual patterns observed during the mescaline experience include stripes , checkerboards , angular spikes , multicolored dots , and very simple fractals which turn very complex. Objects can appear flattened and distorted, similar to the presentation of a Cubist painting (10).
- Step 3, entheogenic effects : comprehend feelings of inner peace and tranquility, oneness with life, a sense of union with “the cosmos,”;other effects include *+euphoria+ and dream-like state and rapid thought flow (11). The action of mescaline on the optic nerve produces synesthesia (overlapping of senses).

As physiological side effects ,in such cases users may suffer bloody diarrhea and fall into unconsciousness . Mescaline assumption can cause headache or dizziness: headache pain can range in severity from mild to severe and can negatively affect a person's ability to concentrate (13). Sensations of dizziness and profuse sweating can cause a person to appear unstable or confused while walking or standing .People who take mescaline can experience involuntary or uncoordinated muscle movements.
Moods and states of mind before mescaline consumption can deeply influence these kind of experiences, inducing good or bad trips: a bad trip is considered as a side effect because good feelings usually related with mescaline intake are substituted by anxiety and fear that can turn in a panic attack with uncontrolled trembling or convulsions .
However mescaline doesn’t provoke tolerance or addiction it can make psychological problems never diagnosed before surface in the users. The acute toxicity of peyote or mescaline is not as high as it is for several other alkaloids (14), but a case of a fatality because of trauma during drug-induced delirium and another caused by a traumatic injury to the esophagus secondary to vomiting have been described (15). Lethal doses produce convulsions , breath-arrests and heart failures bringing mescaline abuser to death .